text: This is the case of a vortex filament rotating at constant speed, there is a cylindrical symmetry and the problem can be solved in the orthogonal plane.
  Dual to the case above of line sources, vortex lines play the role of monopoles for irrotational flows.
  Also in this case the flow is also both irrotational and incompressible and therefore a case of potential flow.
  This is characterized by a cylindrical symmetry:
  Where the total circulation is constant for every closed line around the central vortex 
  and is zero for any line not including the vortex.
  Therefore,
  This is derived from a stream function
  or from a potential function
  Which is dual to the previous case of a line source